Field of the Invention
The present invention relates to a crosslinkable fluorine-containing elastomer composition and a molded article made of the composition.
Description of Related Art
Fluorine-containing elastomers, particularly perfluoroelastomers predominantly comprising a tetrafluoroethylene (TFE) unit are widely used as sealing materials, etc. to be used under harsh environment because of excellent chemical resistance, solvent resistance and heat resistance thereof.
However, with advances in technologies, more rigorous demand for characteristics required have been imposed, and in the fields of aviation and space industries, semiconductor manufacturing equipment, and chemical plant, sealing property under higher temperature environment of not less than 300° C. is demanded. The use of a sealing material under such a high temperature environment induces partial deterioration of a polymer, and accelerates generation of hydrogen fluoride (HF). It is conjectured that HF generated at high temperature not only has an adverse effect on materials coming into contact with the polymer but also attacks a molecular chain and a cure site of an elastomer, thus giving adverse effect on them.
So far, trial has been made to reduce generation of HF by adding silicic acid anhydride (SiO2) (JP2002-515525A) to a fluorine-containing elastomer. While generation of HF is sufficiently reduced by such a method, since SiO2 has a lot of functional groups on its surface, control of water amount is difficult, which is a factor of generating outgas resulting from water. In addition, when a large amount of SiO2 is blended, there is delay of curing in crosslinking reaction.
In semiconductor manufacturing process, CVD equipment, etching equipment and ashing equipment are used in steps for forming an insulating film and a thin film for metallic wire. In such equipment, elastomeric sealing materials are used for sealing of various connecting parts and movable parts thereof. These sealing materials are required to have not only sealing property but also plasma resistance for O2 and fluorine-containing gases, and in order to meet requirements for fine fabrication and large size substrate wafer, are also required to withstand harsh conditions for plasma treatment such as high density (1012 to 1013/cm3) and not to contaminate semiconductors to be subjected to very precise processing. Crosslinkable fluorine-containing elastomers are used as elastomeric materials for sealing materials being capable of satisfying such requirements. Further, in order to achieve more sufficient mechanical strength as compared with the case of crosslinking an elastomer alone, usually organic or inorganic filler is blended to an elastomer. Examples of fillers which have been used or proposed are carbon black, silica (Japanese Patent No. 2783576 and Japanese Patent No. 2858198), polytetrafluoroethylene (PTFE) powder, perfluoroalkoxyalkane (PFA powder), titanium oxide powder and barium sulfate.
In addition, in semiconductor manufacturing process, there is a wet process for washing a wafer by using ozone (O3) water. Accordingly, sealing materials are required to be stable in not only NF3 plasma treatment but also O3 treatment.
However, among the above-mentioned fillers, fillers such as silica and titanium oxide are stable in O3 treatment but are subject to decomposition in NF3 plasma treatment, resulting in weight reduction. On the other hand, fillers such as carbon black and PTFE powder are stable in NF3 plasma treatment but are subject to decomposition in ozone treatment, resulting in weight reduction.
In order to eliminate the mentioned problems, WO 03/051999 proposes to blend fillers such as compounds having a specific surface area of not less than 0.5 m2/g and containing an aromatic ring and non-oxide fillers such as borides, carbides, nitrides, silicides, sulfides and phosphides. In this proposal, effect of improving resistance to NF3 remote plasma and resistance to O3 appears, but there is still room for improvement in minimizing weight reduction and inhibiting generation of particles in high density plasma treatment using O2 gas and fluorine-containing gas.